Colors of the Rainbow
By Frederick E. Tilton, M.D.; Federal Air Surgeon
Reprinted with permission from FAA Safety Briefing
Most of us take vision—including our ability to see colors—for granted. As you might remember from ground school, the retina holds two kinds of photoreceptor cells: rods and cones. The rods are highly sensitive to light so they help a person see in dim light situations but they cannot differentiate between colors. Three types of cones (red, blue, and green) provide the ability to perceive color.
The condition commonly called “color blindness,” more accurately known as color vision deficiency, is usually an inherited condition caused by a defect in one or more of the cones, and it occurs more commonly in males. However, some pathological conditions can also affect a person’s ability to see color.
Shades of Color Vision
There are several types of color vision deficiency, and complete color vision deficiency is quite rare. Partial color blindness can be divided into two types: red-green and blue-yellow. Red-green deficiencies are caused by a lack of either red or green cones. Blue-yellow deficiencies are caused by missing or defective blue cones. They are far less common, and they tend to have less impact on an individual’s everyday life.
Because a pilot’s world is involved with reds and greens, especially when it comes to night flying, evaluation of an individual’s color vision is a required part of the aviation medical exam. Color vision deficiency is a problem, but it is not necessarily the end of the road for an aspiring aviator.
An airman suffering from some forms of color vision deficiency may still be eligible for an unrestricted medical certificate if he or she can pass an operational test. For others, however, it may result in a limitation stating that the certificate is “not valid for night flying or by color signal control.” So, if a person fails to pass the color vision part of their medical examination while in their AME’s office, he or she can appeal to the FAA for additional operational testing. The FAA will work with the airman to determine the extent of the airman’s capabilities in color-dependent situations. If the airman successfully completes this evaluation, the FAA will issue a Letter of Evidence (LOE) that modifies or removes the limitation.
Frederick E. Tilton, M.D., M.P.H., received both an M.S. and an M.D. degree from the University of New Mexico and an M.P.H. from the University of Texas. During a 26-year career with the U.S. Air Force, Dr. Tilton logged more than 4,000 hours as a command pilot and senior flight surgeon flying a variety of aircraft. He currently flies the Cessna Citation 560 XL.